A Search for Clustering around Herbig Ae/Be Stars
It is a well know result that young stars are not found to
form in isolation, but in groups and aggregates. However, while low mass stars
are usually found to form in loose groups with densities of a few stars
per cubic parsecs, high mass stars are known to form in dense clusters
with up to 10000 stars per cubic parsec.
We decided to study the onset of the star formation in clusters
at the intermediate mass level. We have undertaken a survey of a
cospicuous number of fields around intermediate mass young stars
(Herbig Ae/Be stars, HAeBe) with the aim of detect and characterize
the groups of young stars that may have formed together with the HAeBe star.
We chose to observe the fields in the three Near infrared J, H, and K
broad bands following the idea that the clusters we are looking for are
probably embedded in the parental molecular cloud and hence not easily
observable at optical wavelengths.
The observations have been (and are being) carried out using the Arcetri
Near Infrared CAmera (ARNICA)
at the TIRGO
and NOT telescopes.
A few NIR "true color" images from
and K-band images from NOT
are linked at the end of this document.
Up to now 45 fields around HAeBes have been observed. The first results
obtained toward 19 fields have been published in:
Testi L., Palla F., Prusti T., Natta A., Maltagliati S. 1997, A&A, 320, 159
In paper I several cluster identification methods are described and
compared. A Richness Indicator Ic that counts the effective
stars above the background is defined.
From the first sample of 19 objects presented in paper I there is a
hint that the onset of clustering at the intermediate mass level is not
a smooth transition, but detectable clusters appear only around stars
earlyer than B5-B7.
Data reduction and analisys for the whole sample has been completed
and you can check the current Ic vs. Sp.Type
Here are some nice NIR truecolor pictures from the first runs at
LkHa 25 - a confuse field.
LkHa 25 - a nice, tiny group.
BD +404124 - A rich, compact cluster.
And here some from the Aug-Sep 1996 run at
NOT, each image is ~8.5
arcmin wide (K-band):
AS 310 - a preatty crowded field.
BD+651637 - a gorgeous cluster.
HD 200775 - nice nebula!
HD 278937 - a rather empty field.
Last update: 16 May 1997